The present invention relates to a solar energy collection system and particularly to a solar tracking mechanism for a collection system, a method therefor and a solar collection system having a collapsible, light reflective shell.
Solar energy collection systems typically focus sunlight on a radiation absorbing tube or pipe. The focused sunlight heats the fluid in the pipe such that the fluid can be used to generate hot water for residential or commercial use (in homes, office buildings, spas and swimming pools) or used for other applications.
In order to effectively and efficiently collect solar radiation and focus the radiation on the radiation absorbing segment of the tube, the light collection element (typically a light reflective shell) should track the movement of the sun from east to west (the xe2x80x9csolar trackxe2x80x9d of the sun). This solar tracking problem is addressed by the tracking mechanism of the present invention.
Also, it is sometimes necessary or desirable to xe2x80x9cclose-upxe2x80x9d the solar energy collection system. The light reflective surface of the shell is typically delicate or is subject to deterioration in adverse weather. Also, the shell and the system in general can be adversely affected by moderate to strong winds. This problem regarding protecting the light reflective shell (and also protecting the radiation absorbing segment of the tube) is a further subject of the present invention.
U.S. Pat. No. 4,134,387 to Tornstrom discloses low cost solar collectors constructed by stretching this reflective sheet material (such as mirrored plastid) over a frame. U.S. Pat. No. 5,655,515 to Myles, III discloses a solar energy system utilizing an acrylic mirrored surface. U.S. Pat. No. 4,136,671 to Carl L. Whiteford discloses the use of a reflective sheet made of plastic and having a mirror finish. U.S. Pat. No. 5,646,792 to Butler discloses a solar collector utilizing an acrylic mirrored sheet. U.S. Pat. No. 5,325,844 to Rogers et al. disclose a solar panel utilizing acrylic mirrored surfaces. U.S. Pat. No. 4,644,934 to Kaus discloses a solar collector made of a rigid fiberglass reinforced mirrored surface. The reflective coating is a mirrored film. Liquid is utilized in the system to collect the solar radiation. The liquid, not specified, runs to a heat exchanger. U.S. Pat. No. 5,851,309 to Kousa discloses a solar collector with acrylic reflective.
The following patent references show the use of oil as a heat transfer medium for a solar collection system. U.S. Pat. No. 5,592,932 to Yeomans discloses a solar collector utilizing oil. U.S. Pat. No. 4,616,487 to Franklin discloses a solar collector utilizing oil. U.S. Pat. No. 4,505,263 to Nameda et al. disclose a solar collector using oil. Silicone oil is utilized. U.S. Pat. No. 4,473,065 to Bates discloses a solar collector device utilizing oil. U.S. Pat. No. 5,447,147 to Stirbl et al. disclose a solar collector system utilizing oil. However, the disclosure also discusses a working fluid xe2x80x9csteam.xe2x80x9d Clam-shell, collapsible frame designs for solar collectors are shown in the following patent references. U.S. Pat. No. 4,138,994 to Shipley, Jr. discloses a solar collector having a collapsible frame. A generally clam-shell shaped unit is disclosed. U.S. Pat. No. 3,613,659 to Phillips discloses a collapsible solar collector. The collector panels fold upwards and downwards along an imaginary access generally running through an axial post between the collector end pieces. U.S. Pat. No. 4,184,479 to Ratliff discloses the use of panel doors which close to cover reflective surfaces. In one figure, the panel doors are opened and in another figure those doors are closed. U.S. Pat. No. 4,154,219 to Gupta et al. disclose the use of a prism on a sheet to direct light to a collector. U.S. Pat. No. 4,282,394 to Lackey et al. discloses a collapsible solar panel system. U.S. Pat. No. 5,520,747 to Marks discloses a collapsible solar collector. The solar collector collapses by folding support bars together. U.S. Pat. No. 5,090,399 to Tarcici discloses a solar collector which is collapsible by inter-leaved panels. U.S. Pat. No. 5,660,644 to Clemens discloses a collapsible solar collector. As shown in one figure, the unit is collapsible on to itself.
The following patent references show solar tracking systems. U.S. Pat. No. 4,210,463 to Escher discloses a solar tracking system. Tracking systems are generally discussed in certain commercial embodiments as background technology. In the patent disclosure itself, the tracking means is described as something xe2x80x9cwell known in the art.xe2x80x9d U.S. Pat. No. 4,223,214 to Dorian discloses a solar tracking device. Dorian discloses the use of a number of differential photo sensors from which a composite signal is obtained to determine the level of ambient light. When the output of the composite signal changes beyond certain set limits, the tracking system initiates a control signal thereby moving the collected panel. U.S. Pat. No. 4,263,892 to Little et al. disclose a heat or temperature sensitive system utilized to align the reflective surface with respect to the sun. Water is utilized to monitor the temperature. A pair of fluid chambers contain xe2x80x9cair.xe2x80x9d When a pressure difference arises in the trapped air chambers due to a heat differential therein, this difference causes diaphragms to move thereby changing the position of a three way valve assembly with an actuating lever. Water in the camber is utilize to move the solar collector. U.S. Pat. No. 4,283,588 to Zitzelsberger discloses an automatic solar guidance system which is radiation responsive. Expansion bodies are partially shaded on one side such that solar radiation causes one body to move when the other body is blocked in the shade. U.S. Pat. No. 4,306,541 to Morrison et al. disclose a solar powered tracking device. U.S. Pat. No. 5,632,823 to Sharan discloses a solar tracking system which monitors the electrical output of solar cells in order to track the sun. U.S. Pat. No. 4,628,142 to Hashizume discloses a solar tracking mechanism utilizing a shape memory alloy coil. U.S. Pat. No. 4,469,938 to Cohen discloses a solar tracking unit which utilizes control signals from two laterally disposed photo cells. U.S. Pat. No. 4,387,702 to Murphy et al. disclose a solar tracking system wherein an element changes shape in response to heat. The element, a rotating sensor bar changes shape and that shape change is translated into movement. U.S. Pat. No. 4,332,240 to Ward discloses a solar powered tracking device. The sun tracker utilizes solar energy to heat a fluid containing sensor which creates pressure utilized to rotate the collector. U.S. Pat. No. 4,304,221 to Trihey discloses a solar tracking device with heat expandible members. U.S. Pat. No. 4,321,909 to Trihey discloses a solar powered tracking device which moves based upon the differential thermal expansion of certain radial components.
It is an object of the present invention to provide a solar tracking mechanism for a solar energy collection system.
It is another object of the present invention to provide a tracking system with a global ON and OFF sensor and switch system which, when utilized in conjunction with a bank of rechargeable batteries (or at least one such battery), enables the solar energy collection system to operate without additional electrical power (the system is electrically self-sufficient).
It is an additional object of the present invention to configure the solar tracking mechanism with a xe2x80x9chuntxe2x80x9d control which searches for the maximum solar collection angular disposition and then follows the solar track of the sun until sunset or until the global ON and OFF control system signals System OFF (i.e., the system hunts for the best angular disposition of the reflector to capture a maximal amount of sunlight or solar energy).
It is a further object of the present invention to provide a solar energy collection system which is hydraulically driven from a supply of pressurized fluid (and which drains to a low pressure sump or drain). Typically, pressurized water is utilized as the hydraulic fluid. A closed hydraulic control system may also be utilized.
It is an additional object of the present invention to provide a method of tracking the sun with a solar energy collection system.
It is a further object to the present invention to provide a solar energy collection system whereby the light reflective shell can be collapsed onto itself thereby protecting the light reflective portions of the shell and the radiation absorbing segment of the tube carrying the heat transfer fluid or media. In a preferred embodiment, the heat transfer media is oil and preferably silicone based oil.
It is an additional object of the present invention to provide a solar energy collection system wherein after the collapse of the bisected concave shell, the collapsed shell can be rotated relative to the ground plane to a favorable angular position. This favorable angular position is typically parallel to the ground plane.
The solar tracking mechanism is utilized in connection with a solar energy collection system. The collection system includes a light reflective shell shaped to focus solar radiation along a plurality of focal points typically identified as foci. A radiation absorbing segment of a tube is disposed on the optical axis of the shell and at the foci. A heat transfer fluid passes through the radiation absorbing segment of the tube. Light and solar energy, focused by the light reflective shell, strikes the radiation absorbing segment of the tube and heats the fluid in the tube. The shell is pivotally mounted on a support frame. The tracking mechanism includes an actuator mounted between the support frame and the pivotally mounted shell. The actuator has a mechanical output which moves the shell dependent upon fluid flows into and out of the actuator. A solar sensor or detector array is mounted deep within a sighting tube. The sighting tube is fixed to the shell such that a line of sight through the sighting tube is at least parallel to the optical axis of the light reflective shell. The solar sensor generates a sensor signal when the sighting tube is illuminated with solar radiation. Means are provided, typically a mechanically actuated switch, to generate a limit stop signal when the shell reaches a maximum angular position. Typically, this maximum angular position is the maximum westward angular solar sight position for the solar energy collection system. The tracking system also includes an actuator control system generating the fluid flows for the actuator based the sensor signal from the solar sensor and the limit stop signal. The method of tracking the sun includes providing a solar cell array, activating the solar collection system when solar radiation illuminating the array exceeds a predetermined threshold, providing a solar sensor shielded from the solar radiation except for direct, aligned radiation at least parallel to the optical axis of the light reflective shell, pivotally rotating the shell westward with respect to the frame based upon the solar sensor signal, stopping the shell at a maximum angular position (customarily the maximum westward position), rotating the shell eastward after reaching the maximum westward angular position and rotating the shell westward if the shell does not reach the maximum westward angular orientation during a predetermined daylight time period. The solar energy collection system may be further configured to include a light reflective shell having a concave cross-section wherein the shell is bisected into two complementary shell halves. The shell halves are hinged together and removable struts span the concave hollow of the shell maintaining the shell in an open configuration. Upon removal of the struts, the shell halves can be collapsed onto each other thereby protecting the light reflective surface and the radiation absorbing segment of the tube carrying fluid adapted to be heated by the solar radiation.